The present invention relates to a pneumatic booster for use in a brake system of a vehicle.
A tandem pneumatic booster, for example, has a structure as shown in FIG. 6. The pneumatic booster has a shell body 3 comprising a front shell 1 and a rear shell 2. The interior of the shell body 3 is divided by a center shell 4 into two chambers, i.e., a front chamber and a rear chamber. The two chambers divided by the center shell 4 are further divided. That is, the front chamber is divided by a power piston 7 having a diaphragm 5 into a constant-pressure chamber 9, in which a negative pressure is to be introduced, and a variable-pressure chamber 11, in which atmospheric air is to be introduced. Similarly, the rear chamber is divided by a power piston 8 having a diaphragm 6 into a constant-pressure chamber 10, in which a negative pressure is to be introduced, and a variable-pressure chamber 12, in which atmospheric air is to be introduced. The power pistons 7 and 8 are provided with a mutual valve body 13. The valve body 13 extends air-tightly and slidably through a central portion of the center shell 4 and through a reduced-diameter cylindrical portion 2a projecting from the rear of the rear shell 2. The valve body 13 contains a valve mechanism (not shown). The valve mechanism is operated through an input rod 14 movable in response to the actuation of a brake pedal to produce differential pressures between the constant-pressure chambers 9 and 10 on the one hand and the variable-pressure chambers 11 and 12 on the other. The differential pressures propel the front and rear power pistons 7 and 8. Thus, a boosted thrust is transmitted to a master cylinder (not shown) through an output rod 15.
In this type of pneumatic booster, the front shell 1 has a cylindrical portion 1a extending rearward to a considerable extent. The outer peripheral edge of the rear shell 2 is joined to an opening edge 1b of a cylindrical portion 1a of the front shell 1, and these edges are united together, for example, by caulking to form the shell body 3. In the above-described tandem pneumatic booster, the center shell 4 also has a cylindrical portion 4a extending rearward to a relatively large extent. The opening edge 4b of the cylindrical portion 4a of the center shell 4 is disposed in the joint between the front shell 1 and the rear shell 2. Of the two diaphragms 5 and 6 constituting the power pistons 7 and 8, the rear diaphragm 6 has an outer peripheral bead 6a thereof also disposed in the joint between the front and rear shells 1 and 2. It should be noted that the front diaphragm 5 is supported by the shell body 3 in a state where an outer peripheral bead 5a of the diaphragm 5 is disposed between a step portion 1c provided on an intermediate part of the cylindrical portion 1a of the front shell 1 and a shoulder portion 4c at the proximal end of the cylindrical portion 4a of the center shell 4.
In this type of pneumatic booster, the front shell 1 has a cylindrical portion la extending rearward to a considerable extent. The outer peripheral edge of the rear shell 2 is joined to the opening edge 1b of the cylindrical portion 1a of the front shell 1, and these edges are united together, for example, by caulking to form the shell body 3. In the above-described tandem pneumatic booster, the center shell 4 also has a cylindrical portion 4a extending rearward to a relatively large extent. The opening edge 4b of the cylindrical portion 4a of the center shell 4 is disposed in the joint between the front shell 1 and the rear shell 2. Of the two diaphragms 5 and 6 constituting the power pistons 7 and 8, the rear diaphragm 6 has an outer peripheral bead 6a thereof also disposed in the joint between the front and rear shells 1 and 2. It should be noted that the front diaphragm 5 is supported by the shell body 3 in a state where an outer peripheral bead 5a of the diaphragm 5 is disposed between a step portion 1c provided on an intermediate part of the cylindrical portion 1a of the front shell 1 and a shoulder portion 4c at the proximal end of the cylindrical portion 4a of the center shell 4.
The above-described conventional pneumatic booster suffers, however, from the following problems. The cylindrical portion 1a of the front shell 1 and the cylindrical portion 4a of the center shell 4 are each formed in a circular straight cylindrical shape. Therefore, when front shells 1 (1A, 1B and 1C) as constituent parts before assembly are stacked on one another in such a manner that the cylindrical portions 1a of the front shells 1 are mounted on each other, as shown in FIG. 7(A), the stacked condition of the front shells 1 is such that the opening edge 1b of each front shell 1 is only slightly engaged with the edge of the shoulder portion (step portion) 1c of the underlying front shell 1. Similarly, the stack of center shells 4 (4A, 4B and 4C) is, as shown in FIG. 7(B), such that the opening edge 4b of each center shell 4 is only slightly engaged with the edge of the shoulder portion (step portion) 4c of the underlying center shell 4. Regarding the stack of rear shells 2 (2A, 2B and 2C), as shown in FIG. 7(C), no overlap is present except that the reduced-diameter cylindrical portions 2a thereof butt to each other. Thus, all the stacks of front shells 1, rear shells 2 and center shells 4 (these will hereinafter be referred to as xe2x80x9cshell elementsxe2x80x9d) lack in balance, so that the stacked condition of shell elements is difficult to maintain stably Accordingly, handling of the stacked shell elements during storage, transport, etc. is extremely troublesome. Further, a large space is formed between each pair of adjacent shell elements when stacked as stated above, resulting in an increase In volume. Consequently, the storage efficiency and the transport efficiency degrade markedly, causing a large economic loss.
The present invention was made in view of the above-described problems with the prior art.
An object of the present invention is to provide a pneumatic booster designed so that when shell elements as constituent parts before assembly are stacked on one another, an overlap of a predetermined size can be ensured between each pair of adjacent shell elements, thereby making a great contribution to the improvement in handleability and to the improvement in storage efficiency and transport efficiency.
The present invention is applied to a pneumatic booster including a front shell element having a bottom portion and a cylindrical portion (outer cylindrical portion) extending from the edge of the bottom portion. The front shell element further has an inner cylindrical portion projecting in the same direction as the direction of extension of the outer cylindrical portion to receive a master cylinder. The pneumatic booster further includes a rear shell element having a bottom portion and a cylindrical portion (outer cylindrical portion) extending from the edge of the bottom portion. A shell body is formed by uniting together the front shell element and the rear shell element in such a manner that the opening edges of the outer cylindrical portions of the front and rear shell elements on the sides thereof opposite to their respective bottom portions are joined together. A valve body is provided to extend through the rear shell element. The valve body has a valve mechanism therein. A power piston is engaged with the valve body to divide the interior of the shell body into a constant-pressure chamber and a variable-pressure chamber. According to the present Invention, the outer cylindrical portion of the front shell element has at least one reduced-diameter portion smaller in diameter than the opening edge, and the inner cylindrical portion of the front shell element has at least one reduced-diameter portion smaller in diameter than the proximal end edge of the inner cylindrical portion at the bottom portion, so that when a plurality of front shell elements as constituent parts before assembly are stacked on one another, both the outer cylindrical portions and the inner cylindrical portions of adjacent front shell elements are fitted in each other, respectively.
With the above-described structure, when a plurality of front shell elements as constituent parts before assembly are stacked on one another, the outer cylindrical portions of each pair of adjacent front shell elements are fitted in each other with a sufficient overlap therebetween. The inner cylindrical portions of each pair of adjacent front shell elements are also fitted in each other with a sufficient overlap therebetween. Therefore, the stacked condition can be maintained stably. Hence, it is possible to facilitate handling of the stacked front shell elements during storage, transport, etc. Moreover, it is possible to reduce the volume of front shell elements as stacked on one another.
Further, the pneumatic booster according to the present Invention may be arranged as follows. The rear shell element has a bottom portion and an outer cylindrical portion extending from the outer edge of the bottom portion and further has an inner cylindrical portion projecting from the bottom portion in a direction opposite to the direction of extension of the outer cylindrical portion. The outer cylindrical portion of the rear shell element has a reduced-diameter portion smaller in diameter than the opening edge thereof, and the inner cylindrical portion of the rear shell element has at least one reduced-diameter portion smaller in diameter than the proximal end edge of the inner cylindrical portion at the bottom portion, so that when a plurality of rear shell elements as constituent parts before assembly are stacked on one another, both the outer cylindrical portions and the inner cylindrical portions of adjacent rear shell elements are fitted in each other, respectively.
It is desirable in the pneumatic booster according to the present invention that the shell element whose cylindrical portion has a frusto-conical shape as stated above should be provided with a stopper portion for regulating the depth of fitting between the cylindrical portions of each pair of adjacent shell elements as stacked on one another when they are constituent parts before assembly. In this case, the cylindrical portions of the stacked shell elements can be prevented from sticking fast to each other by the stopper portion. Therefore, there is no likelihood that the stacked shell elements will become difficult to separate from each other owing to the wedge effect.